A variety of applications exist today involving the use of fluid solvents or reactants, wherein the presence of dissolved gases, particularly air, is undesirable. One example of such an application relates to mobile phases in high performance liquid chromatography, where the presence of even small amounts of dissolved gases can interfere with the accuracy and sensitivity of the results obtained. In some cases, the dissolved gases can form bubbles in the mobile phase, thereby causing measurement error in chromatographic applications. Furthermore, some dissolved gases can cause deleterious effects on the mobile phase as well as the surrounding componentry. Often times, such detrimental effects caused by the dissolved gases is related to the relative concentration of the gases in the mobile phase. To avoid such effects, the gases are typically removed from the mobile phase through a known degassing process.
An additional issue that exists in present liquid chromatography systems involves the necessity of dampening fluid pressure pulsations flowing through respective flow conduits and through respective chromatographic columns, which pulsations result from uneven draw and discharge from positive-displacement fluid pumps, such as reciprocating pumps. In addition, pulsation upstream from the pump results partially from the opening and closing of the individual gradient proportioning valves. The process of opening and closing blending valves occurs in a relatively short period of time. Displacement of the fluid in a short period of time creates very high instantaneous solvent flow rates. This forms local pressure pulsations which change the valve closing/opening speed and thus detrimentally effects the blending valve dynamic range.
To obtain the most accurate chromatographic measurements possible, fluid (mobile phase) flow through the column and the detector should be nearly constant. Thus, in order to obtain a continuous fluid flow at a substantially constant rate, it is desirable to provide the chromatographic system with a pulse-dampener in the fluid flow conduit between the fluid pump and the column/detector.
Fluid pressure pulsations in liquid chromatography systems may also occur upstream from respective fluid pumps, thereby adversely affecting chromatographic operations upstream from the fluid pump. In many applications, the mobile phase transported through the liquid chromatography system is a blend of multiple solvents. In such embodiments, individual solvent reservoirs are operably connected to a blending valve apparatus to blend desired quantities of the distinct solvents into a unitary mobile phase. Solvent may be drawn from the respective reservoirs into the blending valve apparatus by a downstream fluid pump, which pump subsequently delivers the blended mobile phase to the remaining chromatographic components. Because of the pulsation characteristics described above, it is desirable to provide mechanisms for dampening such pulsations between the respective solvent reservoirs and the blending valve apparatus, as well as downstream from the blending valve apparatus. Fluid flow pulsations drawn into the blending valve apparatus have the tendency to decrease the accuracy of the blended mobile phase, such that desired ratios of respective solvents comprising the blend may not be accurate. Further, fluid flow pulsations into the blending apparatus can negatively affect physical componentry in the blending valve apparatus, and may decrease the overall life expectancy thereof. It is therefore desirable to provide a pulse-dampening characteristic to the fluid flow conduits connecting such chromatographic components, and particularly between respective fluid reservoirs and a mobile phase blending apparatus.
A number of pulse-dampening techniques have been implemented to provide such flow-dampening characteristics in liquid chromatography applications. For example, fluid has been routed into expandable chambers, wherein a sudden influx of fluid pressure causes the expandable chamber to correspondingly expand, thereby increasing internal volume and absorbing excess fluid pressure to maintain a relatively constant fluid pressure downstream of the expandable chamber. Such flow-dampening devices, however, can result in non-laminar flow patterns, which may result in detrimental formation of gas bubbles in the bulk of the mobile phase. As described above, such gas bubbles can interfere with accurate chromatographic analysis.
Other proposed systems provide dead volumes in the fluid flow pathways, which volumes are not completely filled in standard flow regimes. Upon fluid flow pulsations, however, the dead volumes accumulate the excess fluid flow, thereby mitigating the flow impact downstream of the dead volumes. As with the expandable chambers, however, the dead volumes may act to promote non-laminar flow in the fluid conduits.
Some applications utilize elliptical or flattened tubes as pulse-dampening fluid conduits. Such pulse-dampening tubes are sufficiently flexible to change in cross-sectional profile when a fluid pulse is directed through the tubes. Typical applications, however, surround the flexible tubing with restraining means for limiting the extent of cross-sectional distention. Such restraining means act against change in cross-sectional profile of the fluid conduits so that the fluid conduits return to an elliptical or flattened profile after the fluid pulse has been dampened. Such restraining means include biasing means, external bodies, and compressible fluids surrounding the fluid conduits.
In addition, the flow-dampening systems proposed to date fail to address the degassing issue in liquid chromatography applications as described above. A particular method of degassing mobile phases includes the use of semi-permeable synthetic polymer resin materials as a fluid conduit material, and the exposure of such a semi-permeable conduit to a reduced pressure or vacuum environment. To perform the degassing, the fluid to be degassed is caused to flow through the conduit in the reduced pressure environment, which allows the dissolved gases to escape from the mobile phase through the semi-permeable conduit walls. By addressing both the degassing functions and the flow-dampening functions in a single apparatus, increased chromatographic efficiency and reduced-sized chromatographic instruments may be achieved.
A further issue in liquid chromatography systems, particularly in systems incorporating multiple mobile phase streams, involves degassing each mobile phase stream between a respective mobile phase reservoir and a blending or proportioning valve for delivery of a mixed mobile phase composition to the fluid pump. Degassing systems available today separately degas each mobile phase stream through various methods, and subsequently deliver each mobile phase stream to a separate blending valve apparatus. Such configurations require multiple distinct degassing units, for example distinct vacuum degassing chambers. The multiplicity of degassing units increases overall size of the system, which correspondingly increases the length of tubing required downstream of the respective degassing chambers, and connecting the respective degassing chambers to a blending valve apparatus. Relatively long transport conduits extending between respective degassing chambers and a blending valve apparatus increases the opportunity for regassing of the mobile phase, wherein gas undesirably enters the respective mobile phase streams through the semi-permeable tubing prior to the blending valve apparatus. In addition, the relatively long mobile phase conduits incorporating multiple distinct degassing units increases overall cost of manufacturing and operating of this system. Moreover, relatively long mobile phase conduits increase the overall fluid flow restriction therethrough, thereby reducing the effectiveness of the fluid pump, as well as potentially causing inaccurate blending of the respective solvents making up the blended mobile phase.
Accordingly, it is a principle object of the present invention to provide a means for simultaneously degassing multiple mobile phase streams in a single degassing apparatus.
Another object of the present invention is to provide an integrated apparatus having a multiple mobile phase stream degassing chamber and a blending valve device incorporated therein.
A further object of the present invention is to provide a fluid pulse-dampening apparatus having degassing capabilities.
A still further object of the present invention is to provide an unrestrained, substantially elliptical flexible tube for dampening flow pulsations and for degassing fluids passing therethrough.
A yet further object of the present invention is to provide substantially elliptical flexible tubes in a single reduced-pressure chamber for degassing multiple distinct fluids passing through the respective tubes, which tubes further act to dampen fluid pulsations passing therethrough.
Another object of the present invention is to provide a flow-dampening degassing apparatus capable of withstanding fluid pulsations of up to about 100 pounds per square inch.
A still further object of the present invention is to provide a fluid pulse-dampening apparatus having fluid degassing capabilities, wherein the apparatus is substantially configured to maintain laminar fluid flow therewithin.
A further object of the present invention is to provide an integrated degassing chamber and blending valve apparatus including a post-blending polishing loop disposed within the singular degassing chamber.
A yet further object of the present invention is to provide an integrated degassing chamber and blending valve apparatus which inhibits or prevents regassing of the mobile phase through the transfer tubing between the respective solvent reservoirs and the blending valve apparatus.
It is another object of the present invention to provide an integrated degassing chamber and blending valve apparatus that minimizes overall transfer tube volume between the degassing chamber and the blending valve apparatus.